Display device and display device production method

ABSTRACT

A display device has a thin film transistor layer, a light-emitting element layer, and an electron transport layer provided on a light-emitting layer. The light-emitting element layer includes a plurality of light-emitting elements each of which includes a first electrode, a function layer, and a second electrode, and that emit mutually different colors of light. A first hole transport layer contains a hole transport material, and the light-emitting layer contains a quantum dot. The first hole transport layer contains the quantum dot, and a hole transport material having a predetermined molecular weight or higher. The light-emitting layer contains the quantum dot and a ligand coordinating with the quantum dot. The first hole transport layer contains the quantum dot coordinating with the ligand. The ligand coordinates with the quantum dot so as to prevent the hole transport material from being exposed to the light-emitting layer.

TECHNICAL FIELD

The disclosure relates to a display device and a method formanufacturing the display device.

BACKGROUND ART

The development and commercialization of self-emission display deviceshas been recently pursued instead of non-self-emission liquid crystaldisplays. Such a display device, which requires no backlight device, hasa light-emitting element, such as an organic light-emitting diode (OLED)or a quantum-dot light-emitting diode (QLED), provided for each pixel.

Further, such a self-emission display device as described above includesa first electrode, a second electrode, and a function layer locatedbetween the first electrode and the second electrode and including atleast a light-emitting layer. Furthermore, in such display devices, aproposal has been made that includes, for instance, forming at least onelayer included in the function layer, e.g., a light-emitting layer, witha liquid-drop method, such as spin coating or ink-jet application,rather than with an already existing evaporation method in order tomanufacture high-definition display devices inexpensively and easily(see Patent Literature 1 for instance).

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Unexamined Patent Application    Publication No. 2012-234748

SUMMARY Technical Problem

By the way, in such a known display device and method for manufacturingthe display device as described above, the light-emitting layer isformed by, for instance, dropping or applying a solution (droplets)containing a functional material (i.e., a light-emitting material) ofthe light-emitting layer onto a hole transport layer. Further, in theknown display device and method for manufacturing the display device, apixel pattern including a light-emitting layer corresponding to threecolors: R, G and B in combination with photolithography to perform RGBcolor-coding.

Unfortunately, in the known display device and method for manufacturingthe display device, the hole transport layer, provided under thelight-emitting layer, is dissolved by a developing solution that is usedin photolithography and thus cannot be formed accurately with anappropriate thickness in some cases. This sometimes degrades displayperformance in the known display device and method for manufacturing thedisplay device.

In view of the above problem, the disclosure aims to provide a displaydevice and a method for manufacturing the display device that canprevent degradation in display performance even when a light-emittinglayer is formed through photolithography.

Solution to Problem

To achieve the above object, a display device according to thedisclosure is a display device provided with a display region having aplurality of pixels, and a frame region surrounding the display region,the display device including:

a thin-film transistor layer; and

a light-emitting element layer including a plurality of light-emittingelements each including a first electrode, a function layer, and asecond electrode, the plurality of light-emitting elements beingconfigured to emit mutually different colors of light,

wherein the function layer includes a first hole transport layer, and alight-emitting layer provided on the first hole transport layer,

the light-emitting layer contains a quantum dot, and

the first hole transport layer contains the quantum dot, and a holetransport material having a predetermined molecular weight or higher.

The inventors of the disclosure have found out that in the displaydevice configured in the foregoing manner, using a hole transportmaterial having a predetermined molecular weight or higher enables afirst hole transport layer that has an appropriate thickness to beformed accurately even when a light-emitting layer is formed throughphotolithography The disclosure has been accomplished based on thisfinding and can offer a display device that can prevent degradation indisplay performance even when a light-emitting layer is formed throughphotolithography.

Further, a method for manufacturing a display device according to thedisclosure is a method for manufacturing a display device provided witha display region having a plurality of pixels, and a frame regionsurrounding the display region, the display device being provided with athin-film transistor layer, and a light-emitting element layer includinga plurality of light-emitting elements each including a first electrode,a function layer and a second electrode, the plurality of light-emittingelements being configured to emit mutually different colors of light,the method including:

a mixed solution forming step of forming a mixed solution that containsa hole transport material having a predetermined molecular weight orhigher, and a quantum dot;

a mixed solution dropping step of dropping the mixed solution over thefirst electrode;

a phase separation step of subjecting a first hole transport layer and alight-emitting layer to phase separation from the mixed solutiondropped, the first hole transport layer containing the hole transportmaterial and the quantum dot, the light-emitting layer being provided onthe first hole transport layer and containing only the quantum dot;

an exposure step of exposing the first hole transport layer and thelight-emitting layer through irradiation with predetermined light; and

a patterning step of patterning the first hole transport layer and thelight-emitting layer individually into a predetermined shape bysubjecting the first hole transport layer and the light-emitting layerto development using a predetermined developing solution.

In the method for manufacturing the display device configured in theforegoing manner, a mixed solution that contains a hole transportmaterial having a predetermined molecular weight or higher, and aquantum dot is formed in the mixed solution forming step. Further, themixed solution is dropped over the first electrode in the mixed solutiondropping step. Further, the dropped solution undergoes the foregoingphase separation step, exposure step and patterning step sequentially.This enables a first hole transport layer that has an appropriatethickness to be formed accurately even when a light-emitting layer isformed through photolithography. As a result, degradation in the displayperformance of the display device can be prevented.

Advantageous Effect of Disclosure

Degradation in display performance can be prevented even when alight-emitting layer is formed using photolithography.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a configuration of a display deviceaccording to a first embodiment of the disclosure.

FIG. 2 is a sectional view of main components of the display deviceillustrated in FIG. 1 .

FIG. 3(a) illustrates a specific configuration of a function layerillustrated in FIG. 2 , FIG. 3(b) illustrates a quantum dot contained ina light-emitting layer illustrated in FIG. 3(a), and FIG. 3(c)illustrates a detailed example configuration of the light-emitting layerand a hole transport layer both illustrated in FIG. 3(a).

FIG. 4 is a sectional view of a specific example configuration of alight-emitting element illustrated in FIG. 2 .

FIG. 5 is a flowchart showing a method for manufacturing the displaydevice.

FIG. 6 is a flowchart showing a specific method for manufacturing themain components of the display device.

FIG. 7 is a sectional view of a first modification of the displaydevice.

FIG. 8 illustrates main components in a second modification of thedisplay device; FIG. 8(a) is a perspective view of a specificconfiguration of a second electrode in the second modification, FIG.8(b) illustrates a specific configuration of a light-emitting elementlayer in the second modification, and FIG. 8(c) is a graph showing aneffect in the second modification.

FIG. 9 illustrates a specific configuration of a function layer of adisplay device according to a second embodiment of the disclosure.

FIG. 10 illustrates a problem in a comparative example; FIG. 10(a) andFIG. 10(b) respectively illustrate how a light-emitting layer and a holetransport layer are formed in the comparative example and how alight-emitting layer and a hole transport layer are formed in the devicein this embodiment.

FIG. 11 illustrates a specific configuration of a function layer of adisplay device according to a third embodiment of the disclosure.

FIG. 12 illustrates a specific configuration of a function layer of adisplay device according to a fourth embodiment of the disclosure.

DESCRIPTION OF EMBODIMENTS

The embodiments of the disclosure will be detailed based on thedrawings. It is noted that the disclosure is not limited to thefollowing embodiments. Moreover, the term “in the same layer”hereinafter refers to that one layer is formed in the same process step(film formation step) as another layer, the term “under” hereinafterrefers to that one layer is formed in a process step anterior to aprocess step of forming a comparative layer, and the term “over”hereinafter refers to that one layer is formed in a process stepposterior to a process step of forming a comparative layer. Further, thesizes of components within each drawing do not truly reflect theiractual sizes, the actual ratio of size of the components, and otherthings.

First Embodiment

FIG. 1 is a schematic diagram of a configuration of a display deviceaccording to a first embodiment of the disclosure. FIG. 2 is a sectionalview of main components of the display device illustrated in FIG. 1 .FIG. 3(a) illustrates a specific configuration of a function layerillustrated in FIG. 2 , FIG. 3(b) illustrates a quantum dot contained ina light-emitting layer illustrated in FIG. 3(a), and FIG. 3(c)illustrates a detailed example configuration of the light-emitting layerand a hole transport layer both illustrated in FIG. 3(a). FIG. 4 is asectional view of a specific example configuration of a light-emittingelement illustrated in FIG. 2 .

As illustrated in FIG. 1 and FIG. 2 , a display device 2 according tothis embodiment has a base 12, on which a barrier layer 3, a thin-filmtransistor (TFT) layer 4, a top-emission light-emitting element layer 5,and a sealing layer 6 are provided in this order, and the display device2 has a plurality of subpixels SP formed in a display region DA. A frameregion NA, surrounding the display region DA, consists of four sideedges Fa to Fd, among which the side edge Fd is provided with a terminalsection TA formed for mounting electronic circuit boards (e.g., an ICchip and an FPC). The terminal section TA includes a plurality ofterminals TM1, TM2, and TMn (n is an integer equal to or greater thantwo). The plurality of terminals TM1, TM2, and TMn are provided alongone of the four sides of the display region DA, as illustrated in FIG. 1. It is noted that a driver circuit (not shown) can be formed at each ofthe side edges Fa to Fd.

The base 12 may be a glass substrate, or a flexible substrate includinga film of resin, such as polyimide. Further, the base 12 can constitutea flexible substrate using two resin films and an inorganic insulatingfilm interposed between the resin films. Furthermore, a film, such as aPET film, may be attached on the lower surface of the base 12. Further,the display device 2 having flexibility, that is, a flexible displaydevice 2 can be formed when a flexible substrate is used as the base 12.

The barrier layer 3 protects the thin-film transistor layer 4 andlight-emitting element layer 5 from intrusion of foreign substances,including water and oxygen, and can be composed of, for instance, asilicon oxide film, a silicon nitride film, or a silicon oxide nitridefilm, all of which are formed through CVD, or a laminated film of thesematerials.

As illustrated in FIG. 2 , the thin-film transistor layer 4 includes asemiconductor layer (including a semiconductor film 15) over the barrierlayer 3, an inorganic insulating film 16 (gate insulating film) over thesemiconductor layer, a first metal layer (including a gate electrode GE)over the inorganic insulating film 16, an inorganic insulating film 18over the first metal layer, a second metal layer (including a capacitiveelectrode CE) over the inorganic insulating film 18, an inorganicinsulating film 20 over the second metal layer, a third metal layer(including a data signal line DL) over the inorganic insulating film 20,and a flattening film 21 over the third metal layer.

The semiconductor layer is composed of, for instance, amorphous silicon,low-temperature polysilicon (LTPS), or an oxide semiconductor, and thegate electrode GE and the semiconductor film 15 together constitute athin-film transistor TR.

It is noted that this embodiment has described a thin-film transistor TRof a top-gate type by way of example, the thin-film transistor TR may bea bottom-gate thin-film transistor.

The display region DA includes a light-emitting element X and a circuitfor controlling the light-emitting element X, both of which are providedfor each subpixel SP, and the thin-film transistor layer 4 includesthese control circuits and wires connected to them. Examples of thewires connected to the control circuit include, but not limited to, ascan signal line GL and a light-emission control line EM, both formed inthe first metal layer, an initialization power-source line IL, providedin the second metal layer, and the data signal line DL and ahigh-voltage power-source line PL, both provided in the third metallayer. The control circuit includes, but not limited to, a drivetransistor that controls a current that flows through the light-emittingelement X, a write transistor electrically connected to the scan signalline, and a light-emission control transistor electrically connected tothe light-emission control line, all of which are not shown.

The first metal layer, the second metal layer, and the third metal layerare composed of a monolayer or multilayer film of metal including atleast one of, for instance, aluminum, tungsten, molybdenum, tantalum,chromium, titanium, and copper.

The inorganic insulating films 16, 18, and 20 can be composed of, forinstance, a silicon oxide (SiOx) film or a silicon nitride (SiNx) film,both of which are formed through CVD, or can be composed of, forinstance, a laminate of these films. The flattening film 21 can be madeof an organic material that can be applied, such as polyimide or acrylicresin.

The light-emitting element layer 5 includes a first electrode (anode) 22over the flattening film 21, an insulating edge cover film 23 coveringthe edge of the first electrode 22, a function layer 24 over the edgecover film 23, and a second electrode (cathode) 25 over the functionlayer 24. That is, the light-emitting element layer 5 includes aplurality of light-emitting elements X each including the firstelectrode 22, a light-emitting layer (described later on) included inthe function layer 24, and the second electrode 25, and the plurality oflight-emitting elements X emit mutually different colors of light. Theedge cover film 23 is formed by, for instance, applying an organicmaterial, such as polyimide or acrylic resin, followed by patterningthrough photolithography. Further, the edge cover film 23 overlaps theend of a surface of the first electrode 22, which is in the form of anisland, to define a pixel (subpixel SP) and is a bank partitioning aplurality of individual pixels (subpixels SP) in correspondence with theplurality of respective light-emitting elements X. Further, the functionlayer 24 is an electroluminescence (EL) layer containingelectroluminescence elements.

The light emitter layer 5 includes a light-emitting element Xr (red), alight-emitting element Xg (green), and a light-emitting element Xb(blue) all included in the light-emitting elements X and designed toemit mutually different colors of light. Further, each light-emittingelement X includes the first electrode 22, the function layer 24(including the light-emitting layer), and the second electrode 25. Thefirst electrode 22 is an electrode in the form of an island provided foreach light-emitting element X (i.e., the subpixel SP). The secondelectrode 25 is a flat electrode common to all the light-emittingelements X.

The light-emitting elements Xr, Xg, and Xb are, for instance,quantum-dot light-emitting diodes (QLEDs) each including the foregoinglight-emitting layer, which is herein a quantum-dot light-emittinglayer.

The function layer 24 is composed of a stack of, for instance, a holeinjection layer 24 a, a first hole transport layer 24 b, alight-emitting layer 24 c, an electron transport layer 24 d, and anelectron injection layer 24 e in sequence from the bottom, asillustrated in FIG. 3(a). Further, the function layer 24 may include anelectron blocking layer or a hole blocking layer. The first holetransport layer 24 b and the light-emitting layer 24 c are, as describedlater on, dropped onto the hole injection layer 24 a through a dropmethod, where a mixed solution is dropped, and the first hole transportlayer 24 b and the light-emitting layer 24 c undergo phase separationand are then formed in the form of an island in the opening (for eachsubpixel SP) of the edge cover film 23. The other layers are formed inthe form of an island or in a flat manner (common layers). Further, thefunction layer 24 can have a configuration where one or more of the holeinjection layer 24 a, the electron transport layer 24 d and the electroninjection layer 24 e are not formed.

Further, the light-emitting layer 24 c contains quantum dots(semiconductor nanoparticles) 50, as illustrated in FIG. 3(b). Eachquantum dot 50 has a core-shell structure having, for instance, a core51 and a shell 52, which is the outer shell of the core 51. Furthermore,each quantum dot 50 coordinates with ligands 53 each having a long-chainportion 53 a and a coordinating portion 53 b.

Further, the quantum dots 50 are light-emitting materials having avalence band level and a conduction band level, and designed to emitlight upon rejoining between holes of the valence band level andelectrons of the conduction band level, and the quantum dots 50 are eacha single phosphor particle without visible-light scattering. Lightemitted from the quantum dots 50 has a narrow spectrum due to a quantumconfinement effect, and hence, light emission of relatively deepchromaticity can be achieved.

Further, the quantum dots 50 have a particle diameter of about 3 to 15nm. The wavelength of light emitted from the quantum dots 50 can becontrolled by the particle diameter of the quantum dots 50. Hence,controlling the particle diameter of the quantum dots 50 can regulatethe wavelength of light emitted by the display device 2.

Further, the first hole transport layer 24 b contains the quantum dots50, as illustrated in FIG. 3(c). This is because that the mixed solutionis dropped onto the hole injection layer 24 a, followed by phaseseparation, thus forming the first hole transport layer 24 b and thelight-emitting layer 24 c. Further, the first hole transport layer 24 bcontains a hole transport material having a predetermined molecularweight or higher. To be specific, the first hole transport layer 24 bcontains a hole transport material having a molecular weight of 100,000or greater. Furthermore, the first hole transport layer 24 b accordingto this embodiment contains, as described later on, a hole transportmaterial including polymers HTLP of a predetermined hole transportmaterial and a predetermined basic skeleton.

The display device 2 according to this embodiment has a known structure,where, as illustrated in FIG. 2 , the anode (first electrode 22), thefunction layer 24, and the cathode (second electrode 25) are providedsequentially on the thin-film transistor layer 4.

Further, as illustrated in FIG. 4 , the light-emitting elements Xr, Xgand Xb of the display device 2 according to this embodiment arepartitioned by the edge cover film 23, which is a bank, and for eachlight-emitting element X, the first electrode 22 in the form of anisland, the hole injection layer 24 a in the form of an island, thefirst hole transport layer 24 b in the form of an island, andlight-emitting layers 24 cr, 24 cg and 24 cb (generically referred to asthe light-emitting layer 24 c) in the form of islands are provided.Further, the electron transport layer 24 d in a flat manner, theelectron injection layer 24 e in a flat manner, and the second electrode25 in a flat manner, all of which are common to all the subpixels SP,are provided in the light-emitting element X.

Further, in the light-emitting layer 24 c, a drive current between thefirst electrode 22 and the second electrode 25 causes a hole and anelectron to rejoin together within the light-emitting layer 24 c, thusgenerating an exciton, and the exciton emits light (fluorescent light)in the process of transition from the conduction band level of thequantum dot 50 to the valence band level of the quantum dot 50.

The light-emitting element layer 5 may include light-emitting elementsother than the foregoing quantum dots (QLEDs) 50, such as organic ELlight-emitting elements (OLEDs) or inorganic light-emitting diodes.

Further, the following describes an instance where in the display device2 according to this embodiment, the red light-emitting element Xrincludes a red quantum-dot light-emitting layer that emits red light,the green light-emitting element Xg includes a green quantum-dotlight-emitting layer that emits green light, and the blue light-emittingelement Xb includes a blue quantum-dot light-emitting layer that emitsblue light.

The quantum-dot light-emitting layers (light-emitting layer 24 c)contain the quantum dots 50 as a functional material that contributes tothe function of the light-emitting layer 24 c, and the light-emittinglayers 24 cr, 24 cg and 24 cb of the respective colors are configuredsuch that at least the particle diameters of the quantum dots 50 aredifferent from each other in accordance with their light emissionspectrum.

The first electrode (anode) 22 is composed of, for instance, indium tinoxide (ITO), indium zinc oxide (IZO), silver (Ag), or Al or is composedof, for instance, a laminate of Ag-containing alloy and Al-containingalloy, and the first electrode 22 has light reflectivity. The secondelectrode (cathode) 25 is a transparent electrode composed of alight-transparency conductor, including a thin film of Ag, Au, Pt, Ni,Ir or Al, a thin film of MgAg alloy, an ITO, and an indium zinc oxide(IZO). It is noted that a configuration other than the foregoing may beprovided where the second electrode 25 is formed using nanowires ofmetal, such as silver. For forming the second electrode 25, which is aflat common electrode in an upper layer, by the use of such metalnanowires, applying a solution containing the metal nanowires canprovide the second electrode 25. As a result, layers except the firstelectrode 22, that is, the individual layers of the function layer 24and the second electrode 25 can be formed in the light-emitting elementlayer 5 of the display device 2 through a drop method using apredetermined solution, thereby easily forming the display device 2 thatis manufactured simply.

The sealing layer 6 is transparent to light and includes an inorganicsealing film 26 directly formed on the second electrode 25 (in contactwith the second electrode 25), an organic film 27 over the inorganicsealing film 26, and an inorganic sealing film 28 over the organic film27. The sealing layer 6, covering the light-emitting element layer 5,prevents foreign substances, such as water and oxygen, from intrudinginto the light-emitting element layer 5. It is noted that the placementof the sealing layer 6 can be omitted when the light-emitting layer 24 cis composed of a quantum-dot light-emitting layer.

The organic film 27 has a flattening effect and light transparency andcan be formed through, for instance, ink-jet application using anorganic material that can be applied. The inorganic sealing films 26 and28 are inorganic insulating films and can be composed of, for instance,a silicon oxide film, a silicon nitride film, or a silicon oxide nitridefilm, all of which are formed through CVD, or the films can be composedof, for instance, a laminate of these films.

A function film 39 has at least one of the function of opticalcompensation, the function of touch sensing, the function of protection,and other functions.

The following specifically describes a method for manufacturing thedisplay device 2 according to this embodiment with also reference toFIG. 5 . FIG. 5 is a flowchart showing the method for manufacturing thedisplay device.

As illustrated in FIG. 5 , the method for manufacturing the displaydevice 2 according to this embodiment includes, firstly (Step S1),forming the barrier layer 3 and the thin-film transistor layer 4 ontothe base 12. The next (Step S2) is forming the first electrode (anode)22 onto the flattening film 21 through, for instance, sputtering andphotolithography. The next (Step S3) is forming the edge cover film 23.

The next (Step S4) is forming the hole injection layer (HIL) 24 athrough a drop method, such as an ink-jet method. To be specific,examples of a solvent contained in a hole-injection-layer formingsolution in this step of forming a hole injection layer include ethanol,2-propanol, ethylene glycol, polyethylene glycol, butyl benzoate,toluene, chlorobenzene, tetrahydrofuran, and 1,4-dioxane. Further,polythiophene conductors, such as PEDOT:PSS, or inorganic compounds,such as a nickel oxide and a tungsten oxide, for instance, are used as asolute contained in the hole-injection-layer forming solution, that is,as a hole injection material (functional material). Moreover, this HILlayer forming step includes baking the hole-injection-layer formingsolution dropped onto the first electrode 22 at a predeterminedtemperature to thus form the hole injection layer 24 a having athickness of, for instance, 20 to 50 nm.

The next (Step S5) is forming the first hole transport layer (HTL) 24 bthrough a drop method, such as an ink-jet method, and forming (Step S6)the light-emitting layer 24 c at substantially the same time as thefirst hole transport layer 24 b.

Here, the step of forming the first hole transport layer and the step offorming the light-emitting layer will be detailed with also reference toFIG. 6 . FIG. 6 is a flowchart showing a specific method formanufacturing the main components of the display device.

Step S5, i.e., the step of forming the first hole transport layer andStep S6, i.e., the step of forming the light-emitting layer include, asshown in Step SM in FIG. 6 , a preliminary process step, which is hereina mixed solution forming step of forming a mixed solution for formingthe first hole transport layer 24 b and light-emitting layer 24 c. To bespecific, the mixed solution forming step uses, for instance, toluene orpropyleneglycol monomethyl ether acetate (PGMEA) as a solvent of themixed solution.

Further, a hole transport material including, for instance, polymersHTLP of a predetermined hole transport material and a predeterminedbasic skeleton is used as a hole transport material (functionalmaterial) of a solute contained in the mixed solution. To be specific,the polymers HTLP of the predetermined hole transport material areselected from the group consisting of, for instance,Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)] (TFB),Poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] (poly-TPD), andPoly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(N,N′-bis{4-butylphenyl}-benzidine-N,N′-{1,4-diphenylene})](hereinafter, abbreviated as DTFB). Further, triphenylamine and atriphenylamine derivative, for instance, are selected as thepredetermined basic skeleton. To be more specific, the polymers HTLPeach incorporate, for instance, triphenylamine indicated in Chemical 1below or two pieces of triphenylamine indicated in Chemical 2 below.

Herein, X in Chemical 1 has a fluorene group and a triphenylamine group,and X in Chemical 2 has a fluorene group.

Further, the quantum dots 50 containing, for instance, C, Si, Ge, Sn, P,Se, Te, Cd, Zn, Mg, S, In, or O are used as a light-emitting material(functional material) of the solute contained in the mixed solution.Further, dodecanethiol, oleylamine, or oleic acid, for instance, is usedas the ligands 53.

The next is a mixed solution dropping step, as shown in Step S52 in FIG.6 . In the mixed solution dropping step, the foregoing mixed solution isdropped over the first electrode 22, to be specific, onto the holeinjection layer 24 a.

The next is a phase separation step, as shown in Step S53 in FIG. 6 . Inthe phase separation step, the first hole transport layer 24 b,containing the foregoing hole transport material and the quantum dots50, and the light-emitting layer 24 c, provided on the first holetransport layer 24 b and containing only the quantum dots 50, undergophase separation from the dropped mixed solution. Further, the phaseseparation step includes, for instance, allowing the mixed solutiondropped onto the hole injection layer 24 a to stand for a predeterminedtime to thus separate and form the first hole transport layer 24 b andthe light-emitting layer 24 c from the mixed solution. The solventwithin the mixed solution is vaporized to become almost lost during thephase separation step. It is noted that other than this description, thesolvent may be dried along with phase separation through, for instance,pre-baking.

The next is an exposure step, as shown in Step S54 in FIG. 6 . Theexposure step includes exposing the first hole transport layer 24 b andthe light-emitting layer 24 c through irradiation with predeterminedlight (e.g., ultraviolet light). The irradiated portion of the firsthole transport layer 24 b solidifies in the exposure step. This formsthe first hole transport layer 24 b having a thickness of, for instance,20 to 50 nm. Furthermore, as a result of the exposure step, thelight-emitting layer 24 c solidifies as well in a portion (i.e., aportion irradiated with light) located on the solidified first holetransport layer 24 b. This forms the light-emitting layer 24 c having athickness of, for instance, about several nanometers.

The next is a patterning step, as shown in Step S55 in FIG. 6 . Thepatterning step includes patterning the hole transport layer 24 b andthe light-emitting layer 24 c individually into a predetermined shape bysubjecting the first hole transport layer 24 b and the light-emittinglayer 24 c to development using a predetermined developing solution(e.g., toluene). That is, the unsolidified portion of the first holetransport layer 24 b and the unsolidified portion of the light-emittinglayer 24 c are removed in the patterning step.

Then, the mixed solution forming step, the mixed solution dropping step,the phase separation step, the exposure step, and the patterning step,shown in Step S51 through Step S55, are sequentially performedrepeatedly for each of the colors of emitted light. This forms, asillustrated in FIG. 4 , the light-emitting layer 24 cr of the redlight-emitting element Xr, the light-emitting layer 24 cg of the greenlight-emitting element Xg, and the light-emitting layer 24 cb of theblue light-emitting element Xb. Consequently, in this embodiment, apixel pattern corresponding to three colors: R, G, and B is formed incombination with a drop method and photolithography, thus completing RGBcolor-coding.

Referring back to FIG. 5 , the next (Step S7) is forming the electrontransport layer (ETL) 24 d through a drop method, such as an ink-jetmethod or spin coating. To be specific, this step of forming theelectron transport layer uses, for instance, 2-propanol, ethanol,toluene, chlorobenzene, tetrahydrofuran, or 1,4-dioxane as a solvent ofan electron-transport-layer forming solution. Further, nanoparticles of,for instance, zinc oxide (ZnO) or magnesium-added zinc oxide (MgZnO) areused as a solute, that is, an electron transport material (functionalmaterial).

The next (Step S8) is forming the electron injection layer (EIL) 24 ethrough a drop method, such as an ink-jet method or spin coating. To bespecific, this step of forming the electron injection layer uses, forinstance, 2-propanol, ethanol, ethylene glycol, polyethylene glycol,toluene, chlorobenzene, tetrahydrofuran, or 1,4-dioxane as a solvent ofan electron-injection-layer forming solution. Further, nanoparticles of,for instance, zinc oxide (ZnO) or magnesium-added zinc oxide (MgZnO) areused as a solute, that is, an electron injection material (functionalmaterial). Further, an organic salt selected from the group consistingof, for instance, quaternary ammonium salt, lithium tetrafluoroboratesalt, and lithium hexafluorophosphate salt is used as an additive, likethe foregoing hole-injection-layer forming solution.

The next (Step S9) is forming, as the second electrode (cathode) 25, athin film of metal, such as aluminum or silver, onto the electroninjection layer 24 e through, for instance, evaporation or sputtering.

The next (Step S10) is forming the inorganic sealing film 26 so as tocover the second electrode 25, followed by applying a material(precursor) of the organic film 27 onto the inorganic sealing film 26through ink-jet application, followed by curing to form the organic film27, followed by forming the inorganic sealing film 28 over the organicfilm 27. This manufactures the display device 2 having thelight-emitting elements Xr, Xg, and Xb of RGB, as illustrated in FIG. 2.

The display device 2 can be manufactured in the foregoing manner.

The display device 2 according to this embodiment configured in theforegoing manner includes the first hole transport layer 24 b composedof a hole transport material having a predetermined molecular weight orhigher. This enables the first hole transport layer 24 b that has anappropriate thickness to be formed accurately in the display device 2according to this embodiment even when the light-emitting layer 24 c isformed through photolithography. As a result, the display device 2 thatcan prevent degradation in display performance can be configured in thisembodiment even when the light-emitting layer 24 c is formed throughphotolithography.

Here, example results of an experiment conducted by the inventors of thedisclosure will be specifically described with also reference to Table1.

TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 1 Example 2 Example 3 Polymer poly-TPD TFB DTFB poly-TPD TFBDTFB Molecular 100,000 100,000 100,000 80,000 80,000 80,000 weight HTLformation ◯ ◯ ◯ X X X Light emission ◯ ◯ ⊚ X X X performance

In this verification experiment, poly-TPD, TFB, and DTFB were preparedas the foregoing polymers HTLP of the hole transport material, as shownin Table 1. Moreover, example 1 to example 3 were formed as products inthis embodiment, with triphenylamine or two pieces of triphenylaminecontained as a basic skeleton, and with the molecular weight adjusted to100,000. Furthermore, comparative example 1 to comparative example 3were formed as comparative products, with no basic skeleton and with themolecular weight adjusted to 80,000. Thereafter, for each of theproducts in this embodiment and each of the comparative products, asolution mixed with a light-emitting material (quantum dots) wasdropped, followed by phase separation to form a first hole transportlayer (HTL) and a light-emitting layer. Furthermore, RGB color-coding,that is, Step S51 through Step S55 in FIG. 6 were performed for each ofR, G and B to provide light-emitting elements of the respective colors:R, G and B.

As shown in comparative example 1 to comparative example 3 of Table 1,when the hole transport material had a molecular weight of less than100,000, which was a predetermined molecular weight, the first holetransport layer (HTL) was not formed accurately. This was because thatthe first hole transport layer (HTL) was eroded by the foregoingdeveloping solution during photolithography in RGB color-coding. As aresult, comparative example 1 to comparative example 3 exhibited aconsiderable reduction in the light emission performance, as shown inTable 1.

In the products in this embodiment in example 1 to example 3 bycontrast, it has been demonstrated that the first hole transport layer(HTL) is not eroded by the developing solution even though three rinsesare performed using the developing solution in RGB color-coding and canbe formed accurately with an appropriate thickness. Furthermore, Table 1has demonstrated that the products in this embodiment can constitute thedisplay device 2 with high light emission performance, and by extension,high display performance.

Table 1 has also demonstrated that as shown in example 3, for a polymerHTLP containing two pieces of triphenylamine, the function of nitrogenatoms contained in its basic skeleton enhances hole transportability,thus enabling the light emission performance to be improved.

As described above, this embodiment has confirmed that degradation indisplay performance can be prevented in the display device 2, whichincludes the first hole transport layer 24 b and the light-emittinglayer 24 c on the first hole transport layer 24 b both formed of a mixedsolution containing the polymers HTPL of a hole transport materialhaving a predetermined molecular weight or higher (100,000) andcontaining the quantum dots 50.

First Modification

FIG. 7 is a sectional view of a first modification of the foregoingdisplay device.

In the drawing, a main difference between the first modification and thefirst embodiment lies in that the hole injection layer 24 a and thefirst hole transport layer 24 b are provided as common layers common toall the subpixels. It is noted that components common to those in thefirst embodiment will be denoted by the same signs, and that thedescription of redundancies between them will be omitted.

In the display device 2 according to the first modification, the holeinjection layer 24 a and the first hole transport layer 24 b are formedin a flat manner to be common to the light-emitting elements Xr, Xg andXb, as illustrated in FIG. 7 . That is, the hole injection layer 24 aand the first hole transport layer 24 b each can be formed not onlythrough such an ink-jet method as described in the first embodiment, butthrough other drop methods, including spin coating.

The first modification with the foregoing configuration can achieve anaction and effect similar to that in the first embodiment. Further, thehole injection layer 24 a and the first hole transport layer 24 b areformed as common layers, thus also enabling simplified process steps formanufacturing the display device 2.

Second Modification

FIG. 8 illustrates main components in a second modification of thedisplay device; FIG. 8(a) is a perspective view of a specificconfiguration of a second electrode in the second modification, FIG.8(b) illustrates a specific configuration of a light-emitting elementlayer in the second modification, and FIG. 8(c) is a graph showing aneffect in the second modification.

In the drawings, a main difference between the second modification andthe first embodiment lies in that the second electrode 25 including anelectron injection layer and an electron transport layer is provided. Itis noted that components common to those in the first embodiment will bedenoted by the same signs, and that the description of redundanciesbetween them will be omitted.

In the display device 2 according to the second modification, the secondelectrode 25 contains metal nanowires, e.g., silver nanowires NW, andzinc oxide (ZnO) nanoparticles NP, which are an electron-injection-layermaterial and electron transport material, as illustrated in FIG. 8(a).That is, the second electrode 25 containing the silver nanowires NW andthe zinc oxide nanoparticles NP is obtained by applying and drying amixed solution with a silver nanowire solution and a zinc-oxidenanoparticle solution mixed at a desired ratio and stirred. To bespecific, a configuration is established where the silver nanowires NWare arranged three-dimensionally on a random basis to allow the silvernanowires NW to pass through the gaps between the zinc oxidenanoparticles NP (an average particle diameter of 1 to 30 nm).

Further, in the display device 2 according to the second modification, aconfiguration is established where the first electrode 22 (anode), theHTL layer (first hole transport layer) 24 b, the light-emitting layer 24c (e.g., a quantum-dot light-emitting layer), and the second electrode(common cathode) 25 including an electron injection layer and anelectron transport layer are provided in this order, as illustrated inFIG. 8(b).

Further, in the configuration illustrated in FIG. 8(a), the area ofcontact between the silver nanowires NW within the second electrode 25and the zinc oxide nanoparticles NP within the second electrode 25,which are electron transport materials, increases; accordingly, FIG.8(c) demonstrates that within a current density of 0 to 50[milliampere/square centimeter], an external quantum efficiency UB(standardized value with respect to a reference value) of thelight-emitting element X in the second modification improves to a muchgreater degree than the configuration illustrated in FIG. 3 , i.e., anexternal quantum efficiency UA (a reference value at each currentdensity=1) of the light-emitting element X including the secondelectrode 25 formed on the electron injection layer (zinc-oxidenanoparticle layer) 24 e, and to a much greater degree than standardizedexternal quantum efficiency Ua (standardized value with respect to areference value) of a light-emitting element having a cathode of atypical silver thin film.

Further, the number of process steps can be reduced when compared to aninstance where the electron transport layer 24 d, the electron injectionlayer 24 e, and the second electrode (common cathode) 25 are formed indifferent process steps.

Further, too many metal nanowires NW reduce the ability of electrontransport to the light-emitting layer 24 c, whereas too few metalnanowires NW increase the value of electrical resistance. Accordingly,the volume ratio of the metal nanowires NW to the ZnO nanoparticles NPis 1/49 to 1/9.

The second modification with the foregoing configuration can achieve anaction and effect similar to that in the first embodiment.

Second Embodiment

FIG. 9 illustrates a specific configuration of a function layer of adisplay device according to a second embodiment of the disclosure. Inthe drawing, a main difference between this embodiment and the firstembodiment lies in that a first hole transport layer is composed ofmonomers of a hole transport material instead of polymers of a holetransport material and is composed of a photopolymerization initiator.It is noted that components common to those in the first embodiment willbe denoted by the same signs, and that the description of redundanciesbetween them will be omitted.

As illustrated in FIG. 9 , a function layer 24 of a display device 2according to this embodiment includes a first hole transport layer 24′.The first hole transport layer 24 b′ contains a hole transport materialincluding monomers HTLM (see FIG. 10 , which will be described later on)of a predetermined hole transport material, and a photopolymerizationinitiator. Further, the monomers HTLM are used in this embodiment, andthus, ligands 53 in a quantum dot 50 contained in a light-emitting layer24 c coordinate with the quantum dot 50 so as to prevent the monomersHTLM from being exposed to the light-emitting layer 24 c.

To be specific, the monomers HTML of the predetermined hole transportmaterial and the photopolymerization initiator, which initiates thepolymerization of the monomers HTML of the hole transport material bylight, for instance, are used as a hole transport material (functionalmaterial) of a solute contained in the foregoing mixed solution.Further, the monomers HTML of the predetermined hole transport materialare selected from the group consisting of, for instance,N4,N4′-Bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4,N4′-diphenylbiphenyl-4,4′-diamine)(OTPD),N4,N4′-Bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyloxy)phenyl)-N4,N4′-bis(4-methoxyphenyl)biphenyl-4,4′-diamine(QUPD), andN,N′-(4,4′-(Cyclohexane-1,1-diyl)bis(4,1-phenylene))bis(N-(4-(6-(2-ethyloxetan-2-yloxy)hexyl)phenyl)-3,4,5-trifluoroaniline)(X-F6-TAPC). The photopolymerization initiator is a cationicphotopolymerization initiator for instance and is selected from thegroup consisting of, for instance,4-octyloxy-phenyl-phenyliodoniumhexafluoroantimonate (OPPI),diaryliodonium special phosphorus-based anion salt (e.g., IK-1), andtriarylsulfonium special phosphorus-based anion salt (e.g., CPI-410S).

Further, quantum dots 50 containing, for instance, C, Si, Ge, Sn, P, Se,Te, Cd, Zn, Mg, S, In, or O are used, like those in the firstembodiment, as a light-emitting material (functional material) of thesolute contained in the mixed solution. Further, each ligand 53 iscomposed of, for instance, an alkyl chain with 13 or more and 18 or lesscarbon atoms contained in the ligand 53, and a predetermined functionalgroup or is composed of, for instance, a univalent unsaturated fattyacid (such as oleic acid) with 13 or more and 18 or less carbon atomscontained in the ligand 53, in order to prevent the hole transportmaterial from such exposure to the light-emitting layer 24 c as earlierdescribed. Further, the functional group is selected from the groupconsisting of, for instance, a carboxylic acid, a thiol, and an amine.However, when an amine is used as the functional group, it is difficultto perform RGB color-coding (i.e., to form light-emitting elements Xr,Xg and Xb) due to a patterning step, which will be described later on;hence, a carboxylic acid or a thiol is preferably used as the functionalgroup in forming the light-emitting elements Xr, Xg and Xb.

Further, a method for manufacturing the display device 2 according tothis embodiment is different from that according to the first embodimentin Step S53 and Step S54 among the process steps shown in FIG. 6 .

That is, in the phase separation step, i.e., Step S53, the first holetransport layer 24 b′, containing the foregoing hole transport materialand the quantum dots 50 coordinating with the ligands 53, and thelight-emitting layer 24 c, provided on the first hole transport layer 24b′ and containing only the quantum dots 50 coordinating with the ligands53, undergo phase separation from the dropped mixed solution. Further,the phase separation step includes, for instance, allowing the mixedsolution dropped onto the hole injection layer 24 a to stand for apredetermined time to thus separate and form the first hole transportlayer 24 b′ and the light-emitting layer 24 c from the mixed solution.Further, the phase separation step includes phase separation into thefirst hole transport layer 24 b′ and the light-emitting layer 24 c withthe ligands 53 preventing the hole transport material from being exposedto the light-emitting layer 24 c. Further, the solvent within the mixedsolution at this time is vaporized to become almost lost. It is notedthat other than this description, the solvent may be dried along withphase separation through, for instance, pre-baking.

Further, the exposure step, i.e., Step S54 includes exposing the firsthole transport layer 24 b′ and the light-emitting layer 24 c throughirradiation with predetermined light (e.g., ultraviolet light). In theexposure step, the foregoing monomers of the hole transport materialundergo polymerization to turn into polymers, and the irradiated portionof the first hole transport layer 24 b′ solidifies. This forms the firsthole transport layer 24 b′ having a thickness of, for instance, 20 to 50nm. Furthermore, as a result of the exposure step, the light-emittinglayer 24 c solidifies as well in a portion (i.e., a portion irradiatedwith light) located on the solidified first hole transport layer 24 b′.This forms the light-emitting layer 24 c having a thickness of, forinstance, about several nanometers. It is noted that in the monomers ofthe hole transport material, not all the monomers undergo polymerization(turn into polymers) as a result of a polymerization reaction, but themonomers of the hole transport material can be extracted even after thedisplay device 2 is completed; thus, this use can be confirmed.

Here, example results of an experiment conducted by the inventors of thedisclosure will be specifically described with also reference to Table2.

TABLE 2 Comparative Example 4 Example 5 Example 6 Example 4 Monomer OTPDQUPD X-F6-TAPC OTPD Molecular weight 100,000 100,000 100,000 80,000 HTLformation ◯ ◯ ◯ X Light emission ◯ ◯ ◯ X performance

In this verification experiment, OTPD, QUPD, and X-F6-TAPC were preparedas the foregoing polymers HTLM of the hole transport material, as shownin Table 2. Then, example 4, example 5, and example 6 were formed asproducts in this embodiment, with their molecular weight adjusted to100,000. Furthermore, comparative example 4 was formed as a comparativeproduct, with its molecular weight adjusted to 80,000. Thereafter, foreach of the products in this embodiment and of the comparative product,a solution mixed with a light-emitting material (quantum dots) wasdropped, followed by phase separation to form a first hole transportlayer (HTL) and a light-emitting layer. Furthermore, RGB color-coding,that is, Step S51 through Step S55 in FIG. 6 were performed for each ofR, G and B to provide light-emitting elements of the respective colors:R, G and B.

As shown in comparative example 4 of Table 2, when the hole transportmaterial had a molecular weight of less than 100,000, which was apredetermined molecular weight, the first hole transport layer (HTL) wasnot formed accurately. This was because that the first hole transportlayer (HTL) was eroded by such a developing solution as earlierdescribed during photolithography in RGB color-coding, like that incomparative example 1 to comparative example 3 described above. As aresult, comparative example 4 exhibited a considerable reduction in thelight emission performance, as shown in Table 2.

In the products in this embodiment in example 4 to example 6 bycontrast, it has been demonstrated that the first hole transport layer(HTL) is not eroded by the developing solution even though three rinsesare performed using the developing solution in RGB color-coding and canbe formed accurately with an appropriate thickness. Furthermore, Table 2has demonstrated that the products in this embodiment can constitute thedisplay device 2 with high light emission performance, and by extension,high display performance.

Here, the following specifically describes another effect of the displaydevice 2 according to this embodiment with reference to FIG. 10 . FIG.10 illustrates a problem in a comparative example; FIG. 10(a) and FIG.10(b) respectively illustrate how a light-emitting layer and a holetransport layer are formed in the comparative example and how alight-emitting layer and a hole transport layer are formed in the devicein this embodiment.

Firstly, a comparative example 100 a illustrated in FIG. 10(a) will bedescribed. In the comparative example 100 a, a solution was prepared asthe foregoing mixed solution in which a solute consisting of monomersHTLM of the foregoing hole transport material, a photopolymerizationinitiator, and quantum dots each coordinating with ligands was dissolvedin toluene (solvent). Here, unlike the device in this embodiment, aligand containing 12 or less carbon atoms, dodecanethiol for instance,was used in the comparative example 100 a. Moreover, in the comparativeexample 100 a, a hole injection layer 124 a was formed on a base 112(first electrode 122). Subsequently, the forgoing solution was droppedonto a hole injection layer 124 b to subject the hole transport layer124 b to phase separation. Next, a sectional image of the comparativeexample 100 a was taken through SEM to thus find that the solution wasseparated into the hole transport layer 124 b and a light-emitting layer124 ca, as illustrated in FIG. 10(a), but the hole transport layer 124 badjacent to the light-emitting layer 124 ca involved an exposed portion124 br of the monomers HTLM of the hole transport material appearing atthe interface between the hole transport layer 124 b and thelight-emitting layer 124 ca. This has revealed that forming, forinstance, an electron transport layer in the comparative example 100 apossibly establishes electrical contact with the electron transportmaterial within the electron transport layer.

In contrast to this, an image of the device in this embodiment was takenthrough SEM to thus demonstrate that even after the phase separationinto the first hole transport layer 24 b′ and the light-emitting layer24 c, phase separation was made into the first hole transport layer 24b′ and the light-emitting layer 24 c with the ligands 53 of the quantumdots 50, illustrated in FIG. 3(b), preventing the monomers HTLM of thehole transport material from being exposed to the light-emitting layer24 c, as illustrated in FIG. 10(b).

Further, Table 3 shows example results of an experiment conducted by theinventors of the disclosure.

TABLE 3 Functional group: carboxylic acid, thiol or amine Number ofcarbon atoms 12 13 14 . . . 17 18 19 Prevention of exposed portion X ◯ ◯◯ ◯ ◯ ◯ Light emission performance X ◯ ◯ ◯ ◯ ◯ X

Table 3 has clearly revealed that when an alkyl chain and an carboxylicacid, a thiol or an amine as a predetermined functional group are usedin a ligand 53 containing 12 or less carbon atoms, the monomers HTLM ofa hole transport material, such as OTPD, has an exposed portion, thusdegrading light emission performance. Table 3 has also demonstrated thata ligand 53 containing 19 or more carbon atoms degrades the holetransportability of the first hole transport layer 24 b′, thus degradinglight emission performance. That is, it has been revealed that too manycarbon atoms in a long-chain portion 53 a of the ligand 53 hinder holetransport.

In contrast to this, it has been revealed that a ligand 53 containing 13or more and 18 or less carbon atoms prevents such an exposed portion asearlier described and also prevents degradation in holetransportability, thus offering the display device 2 with high lightemission performance, and by extension, high display performance.Further, using a univalent unsaturated fatty acid, such as oleic acid,as the predetermined functional group obtained the same experimentresult as the forgoing thiol and other materials.

This embodiment with the foregoing configuration can achieve an actionand effect similar to that in the first embodiment. Further, in thedisplay device 2 according to this embodiment that includes the firsthole transport layer 24 b′ and the light-emitting layer 24 c on thefirst hole transport layer 24 b′, both formed of a mixed solutioncontaining the quantum dots 50 each coordinating with the ligands 53,containing the monomers HTLM of a hole transport material, such as OTPD,and containing a photopolymerization initiator, it has been revealedthat forming the ligands 53 shown in Table 3 and other things canprevent degradation in display performance.

Third Embodiment

FIG. 11 illustrates a specific configuration of a function layer of adisplay device according to a third embodiment of the disclosure. In thedrawing, a main difference between this embodiment and the secondembodiment lies in that a second hole transport layer is providedbetween a first electrode and a first hole transport layer. It is notedthat components common to those in the second embodiment will be denotedby the same signs, and that the description of redundancies between themwill be omitted.

A display device 2 according to this embodiment has a function layer 24that includes the following on a first electrode 22, as illustrated inFIG. 11 : a hole injection layer 24 a, a second hole transport layer 24f, a first hole transport layer 24 b′, a light-emitting layer 24 c, anelectron transport layer 24 d, and an electron injection layer 24 e.That is, in the function layer 24, the second hole transport layer 24 fis provided between the first electrode 22 and the first hole transportlayer 24 b′.

The second hole transport layer 24 f contains a hole transport materialselected from the group consisting of TFB and poly-TPD. Further, thesecond hole transport layer 24 f is formed, for instance, in a flattermanner to be common to light-emitting elements Xr, Xg and Xb.

Further, a step of forming the second hole transport layer 24 f isperformed before a step of forming the first hole transport layer and astep of forming the light-emitting layer, which are respectively shownas Steps S5 and S6 in FIG. 6 . To be specific, the step of forming thesecond hole transport layer uses, for instance, toluene or chlorobenzeneas a solvent. Further, TFB or poly-TPD is used as a solute, that is, ahole transport material (functional material). Moreover, the step offorming the second hole transport layer includes baking a solutiondropped onto the hole injection layer 24 a at a predeterminedtemperature to thus form the second hole transport layer 24 f having athickness of, for instance, 20 to 50 nm.

This embodiment with the foregoing configuration can achieve an actionand effect similar to that in the second embodiment. Further, thisembodiment, which includes the second hole transport layer 24 f providedbetween the hole injection layer 24 a and the first hole transport layer24 b′ and containing TFB or poly-TPD, enables the highest occupiedmolecular orbital (HOMO) to be formed into a stair-like shape, thusimproving the efficiency of hole transport from the hole injection layer24 a to the first hole transport layer 24 b′.

Fourth Embodiment

FIG. 12 illustrates a specific configuration of a function layer of adisplay device according to a fourth embodiment of the disclosure. Inthe drawing, a main difference between this embodiment and the thirdembodiment lies in that a third hole transport layer is provided betweena first hole transport layer and a second hole transport layer. It isnoted that components common to those in the third embodiment will bedenoted by the same signs, and that the description of redundanciesbetween them will be omitted.

A display device 2 according to this embodiment has a function layer 24that includes the following on a first electrode 22, as illustrated inFIG. 12 : a hole injection layer 24 a, a second hole transport layer 24f, a third hole transport layer 24 g, a first hole transport layer 24b′, a light-emitting layer 24 c, an electron transport layer 24 d, andan electron injection layer 24 e. That is, in the function layer 24, thethird hole transport layer 24 g is provided between the first holetransport layer 24 b′ and the second hole transport layer 24 f.

The third hole transport layer 24 g contains the hole transport materialcontained in the first hole transport layer 24 b′. That is, the thirdhole transport layer 24 g contains monomers of a hole transport materialselected from the group consisting of OTPD, QUPD, and X-F6-TAPC andcontains a (cationic) photopolymerization initiator selected from thegroup consisting of OPPI, diaryliodonium special phosphorus-based anionsalt, and triarylsulfonium special phosphorus-based anion salt. Further,the third hole transport layer 24 g is formed, for instance, in aflatter manner to be common to light-emitting elements Xr, Xg and Xb.

Further, a step of forming the third hole transport layer 24 g isperformed between a step of forming the second hole transport layer,which is described above, and a step of forming the first hole transportlayer as well as a step of forming the light-emitting layer, which arerespectively shown as Steps S5 and S6 in FIG. 6 . To be specific, thestep of forming the third hole transport layer uses, for instance,toluene, chlorobenzene, or propyleneglycol monomethyl ether acetate(PGMEA) as a solvent and uses the foregoing monomers of the holetransport material and the foregoing photopolymerization initiator as asolute. Moreover, a solution containing these solvent and solute isdropped onto the second hole transport layer, and then, like thataccording to the first embodiment, the dropped solution undergoesexposure and then solidification through irradiation with predeterminedlight, to thus form the third hole transport layer 24 g having athickness of, for instance, 20 to 50 nm.

This embodiment with the foregoing configuration can achieve an actionand effect similar to that in the third embodiment. Further, thisembodiment, which includes the third hole transport layer 24 g providedbetween the first hole transport layer 24 b′ and the second holetransport layer 24 f and containing the hole transport materialcontained in the first hole transport layer 24 b′, can improve theefficiency of hole transport between the first hole transport layer 24b′ and the second hole transport layer 24 f and can improve the adhesionbetween their interfaces.

It is noted that other than the foregoing description, the individualembodiments and modifications may be combined as appropriate.

INDUSTRIAL APPLICABILITY

The disclosure is useful for a display device and a method formanufacturing the display device that can prevent degradation in displayperformance even when a light-emitting layer is formed throughphotolithography.

1. A display device provided with a display region having a plurality ofpixels, and a frame region surrounding the display region, the displaydevice comprising: a thin-film transistor layer; and a light-emittingelement layer including a plurality of light-emitting elements eachincluding a first electrode, a function layer, and a second electrode,the plurality of light-emitting elements being configured to emitmutually different colors of light, wherein the function layer includesa first hole transport layer, and a light-emitting layer provided on thefirst hole transport layer, the light-emitting layer contains a quantumdot, and the first hole transport layer contains the quantum dot, and ahole transport material having a predetermined molecular weight orhigher, further comprising an electron transport layer provided on thelight-emitting layer, wherein the light-emitting layer contains thequantum dot and a ligand coordinating with the quantum dot, the firsthole transport layer contains the quantum dot coordinating with theligand, and the ligand coordinates with the quantum dot so as to preventthe hole transport material from being exposed to the light-emittinglayer.
 2. The display device according to claim 1, wherein the firsthole transport layer and the light-emitting layer are formed of a mixedsolution containing the hole transport material and the quantum dot. 3.The display device according to claim 1, wherein the hole transportmaterial has a molecular weight of 100,000 or greater. 4-7. (canceled)8. The display device according to claim 1, wherein the hole transportmaterial contains a monomer of a predetermined hole transport material,and a photopolymerization initiator.
 9. The display device according toclaim 8, wherein the monomer is selected from the group consisting ofOTPD, QUPD, and X-F6-TAPC.
 10. The display device according to claim 8,wherein the photopolymerization initiator is a cationicphotopolymerization initiator.
 11. The display device according to claim10, wherein the cationic photopolymerization initiator is selected fromthe group consisting of OPPI, diaryliodonium special phosphorus-basedanion salt, and triarylsulfonium special phosphorus-based anion salt.12. The display device according to claim 1, wherein the ligand contains13 or more and 18 or less carbon atoms.
 13. The display device accordingto claim 1, wherein the ligand is composed of an alkyl chain and apredetermined functional group.
 14. The display device according toclaim 12, wherein the ligand is composed of a univalent unsaturatedfatty acid.
 15. The display device according to claim 13, wherein thefunctional group is a carboxylic acid or a thiol.
 16. The display deviceaccording to claim 1, wherein a second hole transport layer is providedbetween the first electrode and the first hole transport layer.
 17. Thedisplay device according to claim 16, wherein the second hole transportlayer contains a hole transport material selected from the groupconsisting of TFB and poly-TPD.
 18. The display device according toclaim 16, wherein a third hole transport layer is provided between thefirst hole transport layer and the second hole transport layer.
 19. Thedisplay device according to claim 18, wherein the third hole transportlayer contains the hole transport material contained in the first holetransport layer.
 20. A method for manufacturing a display deviceprovided with a display region having a plurality of pixels, and a frameregion surrounding the display region, the display device being providedwith a thin-film transistor layer, and a light-emitting element layerincluding a plurality of light-emitting elements each including a firstelectrode, a function layer and a second electrode, the plurality oflight-emitting elements being configured to emit mutually differentcolors of light, the method comprising: a mixed solution forming step offorming a mixed solution that contains a hole transport material havinga predetermined molecular weight or higher, and a quantum dot; a mixedsolution dropping step of dropping the mixed solution over the firstelectrode; a phase separation step of subjecting a first hole transportlayer and a light-emitting layer to phase separation from the mixedsolution dropped, the first hole transport layer containing the holetransport material and the quantum dot, the light-emitting layer beingprovided on the first hole transport layer and containing only thequantum dot; an exposure step of exposing the first hole transport layerand the light-emitting layer through irradiation with predeterminedlight; and a patterning step of patterning the first hole transportlayer and the light-emitting layer individually into a predeterminedshape by subjecting the first hole transport layer and thelight-emitting layer to development using a predetermined developingsolution.
 21. The method for manufacturing the display device accordingto claim 20, wherein the mixed solution forming step, the mixed solutiondropping step, the phase separation step, the exposure step, and thepatterning step are sequentially performed repeatedly for each of themutually different colors of light.